Method for manufacturing silicon carbide semiconductor device

A silicon carbide semiconductor device, comprising:

• a silicon carbide substrate having an epitaxial layer;
• a trench formed at said epitaxial layer having a side wall surface, a bottom surface, and a first corner portion between said side wall surface and said bottom surface;
• a gate oxide film on an inner surface of said trench, said gate oxide film including a first portion extending continuously from on said side wall surface to on said bottom surface and a second portion extending from on said first portion located on said bottom surface to on a part of said first portion located on said side wall surface;
• and
• a gate electrode on said gate oxide film to contact said second portion and said first portion located on said side wall surface;
• said first portion covering said first corner portion and having a second corner portion at a side end part of an upper surface of said first portion located on said bottom surface, said second portion covering said second corner portion, said second portion having a third corner portion at a side end part of an upper surface of said second portion, said second portion having a central part, a thickness of said side end part of said second portion being greater than a thickness of said central part of said second portion, and a radius of curvature of said third corner portion being greater than a radius of curvature of said second corner portion.